JakeS2

So, after some time I had time to work on my 'S3' ; we're past the idle problems (she idles nicely if you start her up cold and let her run).

When she is at normal temp she won't start. She cranks over but nothing. Sometimes if you crank and leave the power on she might start with misfire and it sounds like a concrete mill - scary. Haven't listened that for more than one sec at a time. If she cools down she starts up nicely again.

Once she is at normal temp she also stalls if you accelerate fast. If you accelerate nicely she performs ok (and is a blast to drive!)

So far the list of changed items keeps increasing:
- New TPS
- Connections have been cleaned & CRC'd
- New lambda (improved idle a lot)
- New reference sensor
- New DME temp sensor
- Vacuum hoses from ICV to intake manifold changed, improved the perf.
- Injectors cleaned and maintenanced at Bosch car service
- New sparks (Bosch WR7DC+) and distributor cap
- New DME relay

Measurements:
- Tried other set of ignition leads - no noticeable difference
- Pressure in all cylinders ~14bar
- Vacuum leaks *SHOULD* be eliminated. By spraying carb cleaner to vacuum hose connections did not have impact on the idle
- Fuel pressure when cold/warm 3,6-3,8bar
- If you take an ignition lead off while she idles there is ~1s of stumbling but she recovers, is this normal?
- If the wire to ICV is taken off - she shuts down

Remaining parts in the car/engine:
- Ignition coil (from S2 - does 968 share the same type?) & wire to coil
- Distributor
- ICV
- FPR

I'm beginning to run out of options - if it's STILL a vacuum leak where could it be? A cracked intake manifold? Surely this is the last engine I buy from a wrecked car and put into my car without taking the engine apart....

RajDatta

Did you confirm the gap on the speed/reference sensor to make sure it's within spec.
The idle control valve is known to gunk up. That could potentially be a problem as well.
Raj

JakeS2

thanks for the info Raj, we suspect the ICV quite a bit too - but in addition the MAF might be "done" also. We will try exchange parts from my friends car and let's see what is the outcome.

CarbonRevo

Flywheel and ref sensor gap shouldn't matter. Car starts fine when cold, but not when at operating temperature. My S2 does the exact same thing. Sometimes it will start warm but idle like crap and if ANY throttle is applied, it will die.

I'm going to be looking at replacing my fuel pump or the check valve at least. Have a feeling the pump is bad and it only shows when the car is warm and sits. Since the fuel pumps on 944's are external units, they rely directly on the fuel to cool them. While the car is running, the fuel is flowing and cooling the fuel pump down. Once to operating temperature and shut off, there isn't any fuel flowing to cool the motor and it simply won't supply the fuel. Once the car sits and cools down some, the pump functions again. May or may not be the problem, but sounds like a damn good theory to me.

It sure is a pain in the *** when the car won't start!

ps...I might mention that my S2 sat for a while due to the owner not having money for a clutch job. IIRC, he said around 2 years? More then enough time for a fuel pump to go bad.

RajDatta

You also might want to check the cables going to the fuel pump. I have seen the connector corrode and give similar symptoms.
Raj

JakeS2

Ok, did some testing.
Coil:
primary resistance 0.00 - 0.30 ohm, depends how long you keep the DMM wires on (coil separated from car's wiring)
secondary resistance 5,97kOhm on both sides + coil is very hot also...

MAF
Voltages differ 20-40% from the Bosch calibration guidelines (i.e when car running it should be 3-5V and it's 2,5-4!)

..and the story goes on (when we get replacement MAF).

Jfrahm

Hot no-starts are often the coil or the ignition module failing when they get warm. I assume you have simply checked for a strong spark with a spark checker or a gap of 1cm.

-Joel.

JakeS2

Hold on... 968 does not have ignition module does it? We bypassed the unit on the S2 wiring harness (at driver's side behind the front lamp).

Anyway, the MAF running values were like up to 40% off the values from Bosch so my unit is heading to JDS Porsche in UK next monday.

JakeS2

Recorded a video clip showing one of the symptoms:

roll the tape:
http://www.youtube.com/watch?v=DClNoB51lnA

any ideas?

Jfrahm

You are right, the ECU must have the module's functionality integrated into it for the 968. One of my parts sources shows a module for the 968 but Pelican does not, just one for the S2 and 928.

At any rate that is the sort of circuit that can get hot and fail.
-Joel.

JakeS2

Okay, phone call to John Speake at JDSPorsche.com finally showed way to the problem. The MAF was totally giving wrong values so John changed it - now the S3 has a factory exchange "new" MAF - an OEM S2 air filter and new coil... list of problems:
- Warm start , FIXED
- Hot start, FIXED
- Idle surge, FIXED
- Hesitation under acceleration, FIXED

Love it!!! I truly recommend this conversion to any 944 owner. She pulls easy in the urban traffic with low rpms but when you see open road floor it - and she delivers...